Discovery of a New Sea Spider Belonging to the Genus Pycnogonum (Pycnogonida: Pycnogonidae) in the Mesophotic Zone of Jejudo Island, Korea

A new species of the genus Pycnogonum was discovered in the mesophotic zone of Munseom Islet, Jejudo Island, Korea. Pycnogonum (Nulloviger) bifurcatum sp. nov. is the first case of sea spiders in Korean fauna not only included in the subgenus Nulloviger but also collected in the mesophotic zone of Munseom Islet. The new species is morphologically close to Pycnogonum (Pycnogonum) asiaticum and P. (N.) carinatum, sharing the granular integument, the dorsomedian tubercles on the trunk, and the post-ocular tubercle. The new species can be easily distinguished from the congeners by combination of the following characteristics: the prominent dorsomedian tubercles on the trunk, the lateral processes 1-3 touching each other, and the small auxiliary claws. A key is provided to distinguish 12 species of the subgenus Nulloviger morphologically, and molecular data of the new species are provided for species identification and further studies.